The present invention relates to a cleaning apparatus capable of effectively removing residual part of a toner which is left non-transferred on the surface of a photoconductive element, which serves as an image support in an electrophotographic copier or the like. More particularly, the present invention relates to an improved magnet brush cleaning apparatus which promotes efficient collection of the residual toner from a magnetic carrier which constitutes a cleaning agent, saves consumption of the carrier, prolongs the service life of the carrier, and permits the carrier to be automatically replenished and replaced.
Various systems have heretofore been proposed for the removal of a residual toner from a photoconductive element or like image support such as one using a fur brush, a blade and a webbing, or a magnet brush. In the magnet brush type system, a magnet brush of magnetic carrier or the like may be magnetically formed on a rotary sleeve located adjacent to the photoconductive element. In this case, the residual toner magnetically deposited on the magnet brush will be electrostatically transferred onto a collector roller in the vicinity of the sleeve and then scraped off the collector roller by a blade or the like.
In this type of cleaning system, the transfer of the toner from the sleeve to the collector roller is facilitated by the application of a bias voltage opposite in polarity to a charge deposited on the toner across the sleeve and the use of a conductive collector roller which is impressed with a second bias voltage higher than the first. Where the bias voltage to the sleeve lies within the range of 200-400 V, for example, the bias voltage to the collector roller has to be as high as about 600-800 V. Such a high bias voltage to the collector roller tends to cause a leak current to flow from the collector roller to a support system associated therewith. This requires sure insulation and other countermeasures which result in various limitations in practical use.
Meanwhile, what separates the residual toner from the magnet brush or carrier is the mere electrostatic attraction exerted by the collector roller. The toner, therefore, will soon accumulate on the periphery of the magnet brush or carrier thereby rendering the carrier incapable of attracting any more residual toner. Thus, apart from the limited life of the carrier, the accumulation of the toner lowers the frictional charging ability of the carrier to thereby noticeably deteriorate the cleaning efficiency. Furthermore, in a two-component dry-process developing system, the magnetic carrier for cleaning is usually common in quantity and kind to the carrier for development, e.g. iron powder. However, the life or durability of the carrier has been limited to about 10,000-100,000 copies/kg due to the deterioration to the charging ability of the carrier caused by the so-called "toner filming" or the like, introduction of various alien particles such as broken carrier particles and paper powder, etc.
Additionally, because the carrier is liable to adhere to the collector roller and therefore to enter the collected toner by a substantial amount, not only the collected toner tends to become non-reusable but the consumption of the carrier tends to be significantly increased. The result is the need for frequent services for replacing the carrier with fresh one at the sacrifice of economy.
The blade and webbing type cleaning apparatus, which is another known type of apparatus, is undesirable because the blade or the webbing is held in sliding contact with the surface of a photoconductive element to damage the surface of the latter at a significant rate. The fur brush type cleaning apparatus, on the other hand, suffers from the drawback that the life of the photoconductive element is limited by the toner which tends to remain as a thin film on the surface of the photoconductive element even after moved past the cleaning apparatus, i.e. toner filming.